difference() {
    sphere(r = 10);
    translate([0, 0, 5]) cube([15, 15, 15], center = true);
}

translate([25, 0, 0]) {
    union() {
        cylinder(h = 20, r = 5, center = true);
        rotate([90, 0, 0]) cylinder(h = 20, r = 5, center = true);
        rotate([0, 90, 0]) cylinder(h = 20, r = 5, center = true);
    }
}